Microwave ovens operate on the principle that foods respond directly to microwave energy by converting the microwave to thermal energy. Microwave ovens are based upon this simple principle and, in their most basic operational form, are nothing more than a magnetron for converting electrical energy to microwave energy and a means for directing and distributing the microwave energy to an oven cavity. Microwave ovens have become a common, nearly standard appliance in most residential homes as well as most commercial and institutional businesses. The popularity of microwave cooking is attributable mainly to the high speed with which cooking occurs and its ability to reheat foods without causing additional browning/crispen of the food.
A microwave accessory, known as a microwave susceptor, is commonly employed when microwaving foods which need to reach a surface temperature in excess of the surface temperature attainable by unassisted microwaving. A microwave susceptor assists in the microwave cooking of foods by absorbing microwave energy, converting the absorbed microwave energy to thermal energy, and then transferring the thermal energy to the food by means of conduction and/or convection. Susceptors permit microwave ovens to cook many foods once thought to require a conventional oven such as popcorn and pizza, However, one group of foods where susceptors did not perform well was with respect to those foods requiring browning and crisping, such as potatoes, meats and breaded foods. It was believed that microwave energy was able to cook such foods so rapidly by direct absorption that the susceptor did not have an opportunity to brown and/or crispen the food before cooking was complete.
Attempts to increase the amount of heat generated by a susceptor which is available to brown/crispen a food item have met with limited success. With respect to the typical vapor deposited microwave heater film, increasing the useful heat generating capacity of a susceptor by increasing the thickness of the heat generating layer is generally limited by the phenomena that absorptive layers of greater than a specified thickness, based upon the particular material involved as well as various other factors, tend to cause arcing. Likewise, increasing the useful heat generating capacity of a susceptor by increasing the surface area of the susceptor is limited by the requirement that a susceptor must be in direct contact with or directly underneath the food item to be effective.
To compensate for the differences in cooking rates between direct absorption, of microwave energy and transfer of thermal energy by conduction and/or convection, typical microwave packages which employ a susceptor often include a microwave shield, such as a layer of aluminum foil, to control the amount of microwave energy directly reaching the food within the package. By slowing down cooking of the food from the absorption of microwave energy, the susceptor is given sufficient time to brown/crispen the food. In addition, since conduction transfers heat quicker than convection, microwave packages typically configure the susceptor to maximize direct contact between food and susceptor to speed heat transfer from the susceptor to the food.
The use of microwave shielding, while beneficial in many respects, does have its drawbacks. Two major drawbacks associated with the utilization of microwave shielding are that (i) it slows down microwave heating and can significantly increase cooking time, and (ii) can damage the oven and/or cause burning due to arcing.
Likewise the use of direct contact between food and susceptor to maximize conductive heat transfer is beneficial in many respects, but also has drawbacks. One major drawback associated with direct contact between food and susceptor is that typical susceptors are nonporous and will trap food secretions such as grease and steam between the food and the susceptor and thereby saturate the food with such secretions and reduce conductive heat transfer.
Accordingly, a need exists for a microwave susceptor which is constructed, configured and arranged to (i) increase the speed with which the outer surface of food can be browned/crisped by conduction and/or convection, and (ii) provide for the release of exudate from between food and susceptor so as to prevent the food from becoming saturated with such exudate and prevent the accompanying reduction in conductive heat transfer.